Workstations and other digital video telecommunications equipment typically are equipped with a video display that acquires and displays bitmap images through the telecommunications network from video sources. The video display has a single frame buffer which receives bitmap images from the video sources and stores an image of a display screen. Video data is written to the frame buffer in real-time as it arrives from the video sources. At the same time, the display screen is continuously refreshed from top to bottom by video data in the frame buffer.
We have discovered that, in asynchronous communication systems, it is possible for the display screen refresh to overlap with the writing of data from the network to the frame buffer. Such an overlap causes the display screen to be written partially with data from one frame and partially with data from the next frame. That is, at a given moment, the display screen would show some information that was in the frame buffer before the refresh began and some new information received currently from the network. Overlapping of data in this manner produces undesirable artifacts on the display screen.
Multiparty video teleconferencing will increase the demand for improved video capabilities, such as the capability to simultaneously display multiple windows containing video data from different video sources. However, multiple video sources present further complications to the problem described above. In particular, video data will arrive at the frame buffer at different rates from two or more independent, asynchronous sources, thus increasing the probability that the display screen refresh will overlap with the writing of data from one or more of the video sources to the frame buffer.